The presence of corrosive products, contaminants, metallic particles, oxidation, etc., in fluids such as lubricants can cause problems. For example, contaminants in lubricants can lead to damage of machinery in which the lubricant is utilized, causing unnecessary or accelerated wear on the lubricated members.
Various approaches have been developed to detect conditions such as deterioration or contaminants in fluids. One conventional system described in U.S. Pat. No. 4,646,070 utilizes a pair of capacitor electrodes positioned in a fluid. The fluid serves as a dielectric between the electrodes to develop a frequency voltage signal across the capacitor electrodes. Based on such signal, the dielectric and deterioration of the fluid is determined. This solution suffers from a drawback in that it does not inform a user of the specific type or the magnitude of contamination in the fluid.
U.S. Patent No. 5,262,732 describes a system which utilizes an oscillator circuit coupled to a capacitive sensor. The fluid under test is placed in the capacitive sensor and the oscillator circuit generates a signal having a frequency that increases or decreases depending on the capacitance of the sensor. By analyzing the capacitance (via the oscillator output frequency) over a delay period, deteriorization of the fluid under test is evaluated. The output frequency is sampled over the time period, wherein the output frequency is measured a) with an electromagnet on in a first magnetization direction, b) with the electromagnet on in a second magnetization direction, and c) with the electromagnet off. Corrosion, contamination and ferromagnetic particulate data is deduced by analyzing the oscillator frequency with respect to time over the delay period.
The system described in the aforementioned U.S. Pat. No. 5,262,732 is rather large and cumbersome and does not lend itself to portability. In the field, it would be difficult to transport the device from machine to machine to analyze the lubricant at the location of the machinery, for example. In addition, it is advisable that the capacitive sensor which holds the fluid under test be cleaned carefully prior to each test. Unfortunately, this results in inconvenience as well as increased labor costs, etc.
In view of the aforementioned shortcomings associated with existing systems for analyzing conditions of a fluid such as a lubricant, there is a strong need in the art for a fluid screening device which provides detailed information regarding the particular types of contamination, degree of oxidation or other deterioration, etc. Moreover, there is a strong need in the art for such a screening device which is portable and which does not necessitate frequent cleaning of the sensor.